Wafer processing method

ABSTRACT

A wafer processing method includes a liquid supplying step of supplying a liquid to the front side of a wafer, a close contact making step of pressing a protective film against the front side of the wafer with the liquid interposed therebetween, thereby bringing the protective film into close contact with the front side of the wafer, a protective member fixing step of covering the protective film, with a protective member formed from a liquid resin curable by external stimulus, thereby fixing the protective member through the protective film to the front side of the wafer, a grinding step of grinding the back side of the wafer to reduce the thickness of the wafer, and a peeling step of peeling the protective film and the protective member from the wafer thinned by the grinding step.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wafer processing method for use ingrinding a wafer having asperities formed on the front side.

Description of the Related Art

There is an increasing chance of thinning a wafer before dividing thewafer into device chips, so as to reduce the size and weight of eachdevice chip adapted to be incorporated into various electronic equipmentor the like. For example, the wafer can be thinned by holding the frontside of the wafer on which devices axe formed on a chuck table, rotatinga grinding wheel, and pressing the grinding wheel against the back sideof the wafer to thereby grind the back side of the wafer.

In grinding the wafer by using the above method, a protective member isusually attached to the front side of the wafer (see Japanese PatentLaid-Open Ho. Hei 10-50642, for example), The protective member canprevent the possibility that the devices formed on the front side of thewafer may he damaged by a force applied to the wafer in grinding thewafer. Examples of the protective member include an adhesive tape formedof resin and a substrate having high hardness.

SUMMARY OF THE INVENTION

In many cases, asperities such as bumps functioning as electrodes oneach device are formed on the front side of the wafer. However, whensuch asperities are present on the front side of the wafer, there arisesa problem such that a height difference due to the asperities cannot besufficiently absorbed by an adhesive tape and the shape corresponding toeach asperity may appear on the back side of the wafer after grinding.

By using a substrate having high hardness as the protective member, theabove problem can be almost eliminated. However, this substrate isbonded to the wafer by using an adhesive such as a thermoplastic wax.Accordingly, in peeling the substrate from the wafer after grinding, itis necessary to conduct any extensive work dedicated to peeling, such asimmersion of the wafer in a solution or heating of the wafer at hightemperatures.

It is therefore an object of the present invention to provide a waferprocessing method which can sufficiently suppress the influence of theasperities present on the front side of the wafer in grinding the backside of the wafer and can simply perform a peeling operation aftergrinding.

In accordance with an aspect of the present invention, there is provideda wafer processing method including a liquid supplying step of supplyinga liquid to the front side of a wafer on which a central device area anda peripheral marginal area surrounding the device area are formed, aplurality of devices each having asperities being formed in the devicearea; a close contact making step of pressing a protective film againstthe front side of the wafer with the liquid interposed therebetweenafter performing the liquid supplying step, thereby bringing theprotective film into close contact with the front side of the wafer soas to follow the asperities of each device formed on the front side ofthe wafer; a protective member fixing step of covering the protectivefilm with a protective member formed from a liquid resin curable byexternal stimulus after performing the close contact making step,thereby fixing the protective member through the protective film to thefront side of the wafer; a grinding step of holding the protectivemember fixed to the wafer on a holding surface of a chuck table in thecondition where the back side of the wafer is exposed after performingthe protective member fixing step, and next grinding the back side ofthe wafer to thereby reduce the thickness of the wafer; and a peelingstep of peeling the protective film and the protective member from thewafer after performing the grinding step.

Preferably, the peeling step includes the step of heating the liquidleft between the protective film and the front side of the wafer tothereby vaporize the liquid.

Preferably, the peeling step includes the steps of loading the waferwith the protective member into a vacuum chamber and next evacuating thevacuum chamber to thereby vaporize the liquid left between, theprotective film and the front side of the wafer.

Preferably, the liquid supplying step includes the step of supplying theliquid to a central portion of the front side of the wafer.

Preferably, the protective film has a first surface and a second surfaceopposite to the first surface, the first surface being opposed to thewafer; the close contact making step including the step of discharging agas toward the second surface of the protective film to thereby pressthe protective film against the front side of the wafer.

Preferably, the close contact making step includes the step of using apressure roller to thereby press the protective film against the frontside of the wafer.

Preferably, the protective member fixing step includes the steps ofapplying the liquid resin to a flat sheet, next pressing the waferagainst the liquid resin through the protective film to thereby fullycover the protective film with the liquid resin, and next applying theexternal stimulus to the liquid resin to thereby cure the liquid resin,thereby forming the protective member from the liquid resin and fixingthe protective member to the wafer.

In the wafer processing method according to the present invention, theprotective film is first brought into close contact with the front sideof the wafer on which the devices each having asperities are formed insuch a manner as to follow the asperities. Thereafter, the protectivefilm is covered with the protective member formed from the liquid resincurable by external stimulus, thereby fixing the protective memberthrough the protective film to the front side of the wafer. Accordingly,by forming the protective member having a suitable thickness, theasperities formed on the front side of the wafer can be sufficientlyabsorbed.

In the wafer processing method according to the present invention, theprotective film is not bonded to the device area of the wafer, but ismerely in close contact with the device area. Accordingly, theprotective member and the protective film can be simply peeled from thewafer without the need for any extensive work dedicated to peeling, suchas immersion of the wafer in a solution or heating of the wafer at hightemperatures. Thus, according to the present invention, it is possibleto provide a wafer processing method which can exhibit the effects thatthe influence of the asperities present on the front side of the wafercan be sufficiently suppressed in grinding the back side of the waferand that the peeling operation after grinding can also be simplyperformed.

Further, in the wafer processing method, according to the presentinvention, the protective film is pressed against the front side of thewafer through the liquid supplied to the front side of the wafer.Accordingly, it is possible to prevent that air may be left between thewafer and the protective film, thereby reliably bringing the protectivefilm into close contact with the front side of the wafer. As a result,although the protective film does not have adhesion by an adhesive(paste), there is no possibility that the protective film and theprotective member may be peeled from the wafer in grinding the wafer.

The above and other objects, features and advantages of the presentinvention and the manner of realizing them will become more apparent,and the invention itself will best be understood from a study of thefollowing description and appended claims with reference to the attacheddrawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic perspective view showing a manner of opposing aprotective film to the front side of a wafer;

FIG. 1B is a schematic perspective view showing a condition where theprotective film is in close contact with the front side of the wafer;

FIG. 2A is a schematic sectional view showing a condition where theprotective film is opposed to the front side of the wafer in a closecontact making step according to a preferred embodiment;

FIG. 2B is a schematic sectional view showing a manner of bringing theprotective film into close contact with the front side of the wafer inthe close contact making step;

FIG. 3A is a schematic sectional view showing a condition where theprotective film has been brought into close contact with the front sideof the wafer;

FIG. 3B is an enlarged sectional view of a part of the wafer in thecondition where the protective film is in close contact with the frontside of the wafer;

FIG. 4A is a schematic sectional view showing a manner of pressing thewafer through the protective film against a liquid resin applied to asheet in a protective member fixing step according to this preferredembodiment;

FIG. 4B is a schematic sectional view showing a manner of curing theliquid resin to thereby form a protective member, thereby fixing theprotective member through the protective film to the front side of thewafer in the protective member fixing step;

FIG. 4C is a schematic sectional view showing the wafer in the conditionwhere the protective member supported to the sheet is fixed through theprotective film to the front side of the wafer;

FIG. 5A is a schematic side view, partially in cross section, showing amanner of grinding the back side of the wafer in a grinding stepaccording to this preferred embodiment;

FIG. 5B is a schematic sectional view of the wafer processed by thegrinding step;

FIG. 6 is a schematic sectional view showing a manner of peeling theprotective film and the protective member from the wafer in a peelingstep according to this preferred embodiment;

FIG. 7 is a schematic sectional view showing a manner of peeling theprotective film and the protective member from the wafer in a peelingstep according to a first modification;

FIG. 8 is a schematic sectional view showing a manner of peeling theprotective film and the protective member from the wafer in a peelingstep according to a second modification; and

FIGS. 9A and 9B are schematic sectional views for illustrating a closecontact making step according to a third modification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will now be describedwith reference to the attached drawings. The wafer processing methodaccording to this preferred embodiment includes a liquid supplying step,a close contact making step (see FIGS. 1A, 1B, 2A, 2B, 3A, and 3B), aprotective member fixing step (see FIGS. 4A, 4B, and 4C), and a grindingstep (see FIGS. 5A and 5B), and a peeling step (see FIG. 6). In theliquid supplying step, a liquid is supplied to the front side of a waferon which asperities are formed. In the close contact making step, aprotective film not having adhesion by an adhesive (paste) is broughtinto close contact with the front side of the wafer so as to follow theasperities formed on the front side of the wafer. In the protectivemember fixing step, the protective film is covered with a protectivemember formed from a liquid resin to thereby fix the protective memberthrough the protective film, to the front side of the wafer. In thegrinding step, the back side of the wafer is ground in the conditionwhere the protective member fixed through the protective film to thefront side of the wafer is held on a holding surface of a chuck table.In the peeling step, the protective member and the protective film arepeeled together from the wafer thinned by the grinding step. The waferprocessing method according to this preferred embodiment will now bedescribed in more detail.

In the wafer processing method according to this preferred embodiment,the liquid supplying step is first performed to supply a liquid to thefront side of a wafer on which asperities are formed. Thereafter, theclose contact making step is performed to bring a protective film nothaving adhesion by an adhesive into close contact with the front side ofthe wafer so as to follow the asperities formed on the front side of thewafer. In other words, the protective film is pressed against the frontside of the wafer with the liquid interposed therebetween, therebybringing the protective film into close contact with the front side ofthe wafer. FIG. 1A is a schematic perspective view showing a manner ofopposing the protective film to the front side of the wafer, and FIG. 1Bis a schematic perspective view showing a condition where the protectivefilm is in close contact with the front side of the wafer. FIG. 2A is aschematic sectional view showing a condition where the protective filmis opposed to the front side of the wafer, and FIG. 2B is a schematicsectional view showing a manner of bringing the protective film intoclose contact with the front side of the wafer. FIG. 3A is a schematicsectional view showing a condition where the protective film has beenbrought into close contact with the front side of the wafer, and FIG. 3Bis an enlarged sectional view of a part of the wafer in the conditionwhere the protective film is in close contact with the front side of thewafer. In FIGS. 2A, 2B, and 3A, a part of the components is shown byfunctional blocks.

Referring to FIG. 1A, a wafer 11 to be used in this preferred embodimentis shown. The wafer 11 is a disk-shaped wafer formed of silicon (Si),for example. The wafer 11 has a front side 11 a, a back side 11 b, andan outer circumference 11 c. The outer circumference 11 c is chamferedalong the edges both on the front side 11 a and on the back side 11 b.The front side 11 a of the wafer 11 is composed of a central device area11 d and a peripheral marginal area 11 e surrounding the device area 11d. The device area 11 d is partitioned by a plurality of crossingdivision lines (streets) 13 to thereby define a plurality of separateregions where a plurality of devices 15 such as ICs (integratedcircuits) are individually formed. Further, a plurality of bumps(asperities) 17 functioning as electrodes are provided on the front sideof each device 15. Each bump 17 is formed of solder, for example. Whilethe wafer 11 is a disk-shaped wafer formed of silicon, for example, inthis preferred embodiment, the wafer 11 is not limited in material,shape, structure, size, etc. That is, the wafer 11 may be a wafer formedof any other semiconductors, ceramic, resin, metal, etc. Similarly, thedevices 15 and the bumps 17 are not limited in kind, number, shape,structure, size, layout, etc. The bumps 17 may be replaced by anystructures (asperities) having any other functions. That is, the bumps17 may not be formed on the front side 11 a of the wafer 11, but anyother asperities may be formed on the front side 11 a of the wafer 11.

In the liquid supplying step, a liquid 23 (see FIG. 2A) is supplied tothe front side 11 a of the wafer 11. The liquid 23 to be supplied to thewafer 11 is not especially limited in kind, but it is desirable to use aliquid hard to vaporize at room temperature (20° C.) and having aboiling point not so high (e.g., 100° C. or less). For example, watermay be used as the liquid 23. In this preferred embodiment, the liquid23 is supplied to the center of the front side 11 a of the wafer 11. Asa modification, the liquid 23 may be supplied to another part of thefront side 11 a of the wafer 11 (i.e., any part other than the center ofthe front side 11 a) or may be supplied to the whole of the front side11 a of the wafer 11.

After performing the liquid supplying step, the close contact makingstep is performed to bring a protective film 21 into close contact withthe front side 11 a of the wafer 11 with the liquid 23 interposedtherebetween. The protective film 21 is a flexible film formed of resin,for example. The protective film 21 is a circular member having adiameter substantially equal to that of the wafer 11. Further, theprotective film 21 is not provided with an adhesive. The thickness ofthe protective film 21 is not especially limited. For example, thethickness of the protective film 21 is preferably set to approximately30 μm to 150 μm.

The close contact making step may be performed by using a close contactmaking apparatus 2 shown in FIG. 2A. The close contact making apparatus2 includes a support table 4 for supporting the wafer 11. The supporttable 4 has a substantially flat upper surface, which, functions as asupport surface 4 a for supporting the wafer 11. The support surface 4 ais provided, with a projecting guide portion 4 b for positioning thewafer 11 on the support surface 4 a. There is provided above the supporttable 4 a protective film holding unit 6 for holding the protective film21 under suction and bringing it into close contact with the wafer 11.The protective film holding unit 6 has a substantially flat lowersurface, which functions as a holding surface 6 a for holding theprotective film 21 under suction. The protective film holding unit 6 isvertically movably supported by a moving mechanism (not shown), so thatthe protective film holding unit 6 holding the protective film 21 undersuction can be moved in a vertical direction by operating this movingmechanism.

A first passage 6 b is formed inside the protective film holding unit 6,and one end of the first passage 6 b opens to the holding surface 6 a ina peripheral area for holding the peripheral portion of the protectivefilm 21. The other end of the first passage 6 b is branched into aplurality of portions, more specifically, a first branch portion, asecond branch portion, and a third branch portion. A vacuum source 10 isconnected through a valve 8 to the first branch portion of the firstpassage 6 b. A compressed air source 14 is connected through a valve 12to the second branch portion of the first passage 6 b. Further, a secondpassage 6 c is also formed inside the protective film holding unit 6,and one end of the second passage 6 c opens to the holding surface 6 ain a central area for holding the central portion of the protective film21. The other end of the second passage 6 c is also branched into aplurality of portions, more specifically, a first branch portion and asecond branch portion. The first branch portion of the second passage 6c is connected through a valve 16 to the third branch portion of thefirst passage 6 b. The compressed air source 14 is connected through avalve 18 to the second branch portion of the second passage 6 c.Further, a heater 20 for heating the holding surface 6 a is providedinside the protective film holding unit 6.

In the close contact making step, the wafer 11 is first placed on thesupport table 4 in the condition where the back, side 11 b of the wafer11 is in contact with the support surface 4 a of the support table 4 asshown in FIG. 2A. Accordingly, the wafer 11 is supported on the supporttable 4 in the condition where the front side 11 a of the wafer 11 isexposed upward. Thereafter, the protective film 21 is brought intocontact with the holding surface 6 a of the protective film holding unit6 so as to be aligned with the wafer 11. More specifically, the outercircumference of the protective film 21 is positioned directly above theouter circumference 11 c of the wafer 11. In this condition, the valves8 and 16 are opened to apply a vacuum generated from the vacuum source10 to the protective film 21. Accordingly, the protective film 21 isheld on the holding surface 6 a of the protective film holding unit 6under suction so as to be opposed to the front side 11 a of the wafer11. Before opening the valves 8 and 16, the valves 12 and 18 are closedto stop the supply of compressed air (gas) from the compressed airsource 14 to the first passage 6 b and the second passage 6 c. Thevertical position of the protective film holding unit 6 is adjusted sothat the spacing between the front side 11 a of the wafer 11 and theprotective film 21 becomes approximately 0.1 to 10 mm, for example.

After opposing the protective film 21 to the front side 11 a of thewafer 11, the holding surface 6 a is heated by the heater 20 to therebyapply heat to the protective film 21, thereby softening the protectivefilm 21. Thereafter, as shown in FIG. 2B, the valve 16 is closed to cutoff the vacuum from the vacuum source 10 to the second passage 6 c, andthe valve 18 is next opened to supply the compressed air from thecompressed air source 14 to the second passage 6 c. Accordingly, thecompressed air is discharged toward the central portion of the uppersurface of the protective film 21. In which the central portion of theupper surface of the protective film 21 is merely in contact with theholding surface 6 a at this time (the upper surface of the protectivefilm 21 corresponds to the second surface opposite to the first surfaceof the protective film 21 opposed to the wafer 11). As a result, thecentral portion of the protective film 21 is swelled downward andpressed against the front side 11 a of the wafer 11 as shown in FIG. 28.In this preferred embodiment, the liquid 23 is previously supplied tothe central portion of the front side 11 a of the wafer 11 in the liquidsupplying step as mentioned above, so that the protective film 21 ispressed against the front side 11 a of the wafer 11 with a film of theliquid 23 interposed therebetween.

Thereafter, the discharge of the compressed air toward the protectivefilm 21 is continued, so that the protective film 21 is pressed againstthe front side 11 a of the wafer 11 in a radially outward directionstarting from the center of the wafer 11. After pressing the protectivefilm 21 against the front side 11 a of the wafer 11 in the whole areaexcept the peripheral area yet held under suction, the valve 8 is closedto cut off the vacuum from the vacuum source 10 to the first passage 6b, and the valve 12 is next opened to supply the compressed air from thecompressed air source 14 to the first passage 6 b as shown in FIG. 3A.Accordingly, the compressed air is also discharged toward the peripheralportion of the upper surface of the protective film 21, so that theperipheral portion of the protective film 21 is also pressed against thefront side 11 a of the wafer 11.

As a result, the protective film 21 can be brought into close contactwith the front side 11 a of the wafer 11 so as to follow the shape ofeach bump 17 formed on the front side 11 a of the wafer 11 as shown inFIGS. 1B, 3A, and 3B. Further, in this preferred embodiment, theprotective film 21 is heated to be softened by the heater 20, so thatthe protective film 21 can be brought into close contact with the frontside 11 a of the wafer 11 so as to be properly fitted to each bump 17.Further, when the protective film 21 is pressed against the front side11 a of the wafer 11, the liquid 23 is moved by the protective film 21to push out the air left between the protective film 21 and the frontside 11 a of the wafer 11. Accordingly, the protective film 21 can bereliably brought into close contact with the front side 11 a of thewafer 11 so as to prevent the possibility that the air may be leftbetween the wafer 11 and the protective film 21. In this preferred,embodiment, a film of the liquid 23 is left between the protective film21, and the wafer 11. That is, the protective film 21 is brought intoclose contact with the front side 11 a of the wafer 11 with a film ofthe liquid 23 interposed therebetween.

After performing the close contact making step, the protective memberfixing step is performed to cover the protective film 21 with aprotective member formed from a liquid resin, thereby fixing theprotective member through the protective film 21 to the front side 11 aof the wafer 11. FIG. 4A is a schematic sectional view showing a mannerof pressing the wafer 11 through the protective film 21 against a liquidresin applied to a sheet, FIG. 4B is a schematic sectional view showinga manner of curing the liquid resin to thereby form the protectivemember, thereby fixing the protective member through the protective film21 to the front side 11 a of the wafer 11, and FIG. 4C is a schematicsectional view showing the wafer 11 in the condition where theprotective member supported to the sheet is fixed through the protectivefilm 21 to the front side 11 a of the wafer 11. In FIGS. 4A and 4B, apart of the components is shown by functional blocks.

The protective member fixing step may be performed by using a protectivemember fixing apparatus 22 shown in FIGS. 4A and 4B. The protectivemember fixing apparatus 22 includes a holding table 24 for holding asubstantially flat sheet (carrier sheet) 25 formed of resin, forexample. The holding table 24 has an upper surface formed with a centralcircular recess 24 a larger in diameter than the wafer 11. Anultraviolet light source 26 is provided in the recess 24 a. The upperend opening of the recess 24 a is covered with a plate 28 capable oftransmitting at least a part of ultraviolet, light applied from, theultraviolet light source 26. The sheet 25 is supported at its centralportion by the plate 28. A suction passage 24 b is formed inside theholding table 24 in a peripheral area surrounding the recess 24 a, andone end of the suction passage 24 b opens to the upper surface of theholding table 24 in this peripheral area, so as to hold a peripheralportion of the sheet 25 under suction.

The other end of the suction passage 24 b is connected through a valve30 to a vacuum source 32. Accordingly, by applying a vacuum generatedfrom the vacuum source 32 through the suction passage 24 b to theperipheral portion of the sheet 25, the sheet 25 can be held on theholding table 24 under suction. There is provided above the holdingtable 24 a wafer holding unit 34 for holding the wafer 11. The waferholding unit 34 has a lower surface 34 a for holding the wafer 11. Thewafer holding unit 34 is vertically movably supported by a movingmechanism (not shown), so that the wafer holding unit 34 holding thewafer 11 can be moved in a vertical direction by operating this movingmechanism. The wafer holding unit 34 may be a vacuum suction type suchthat a vacuum is used to hold the wafer 11 under suction or may be of anelectrostatic attraction type such that an electrostatic force is usedto hold the wafer 11.

In the protective member fixing step, a liquid resin 27 is previouslyapplied to the upper surface of the sheet 25 as shown in FIG. 4A, andthe lower surface of the sheet 25 is held on the holding table 24.Further, the back side 11 b of the wafer 11 is held on the lower surface34 a of the wafer holding unit 34. Accordingly, the protective film 21kept in close contact with the front side 11 a of the wafer 11 isopposed to the liquid resin 27 applied to the sheet 25. The liquid resin27 is a liquid resin curable by the ultraviolet light applied from theultraviolet light source 26. For example, TEMPLOC (registered trademark)manufactured by Denka Co., Ltd. may be used as the liquid resin 27.While the sheet 25 is held on the holding table 24 in the conditionwhere the liquid resin 27 is previously applied to the upper-surface ofthe sheet 25 in this preferred embodiment, the sheet 25 only may befirst held on the holding table 24, and the liquid resin 27 may be nextapplied to the upper surface of the sheet 25. As shown in FIG. 4A, theliquid resin 27 is not completely flat on the sheet 25, but the centralportion of the liquid resin 27 is preferably slightly raised.

Thereafter, as shown in FIG. 4B, the wafer holding unit 34 is lowered topress the front side 11 a of the wafer 11 through the protective film 21against the liquid resin 27. As a result, the liquid resin 27 is spreadin the radial direction of the wafer 11 so as to fully cover theprotective film 21. In this preferred embodiment, the amount of theliquid resin 21 to be applied and the amount of lowering of the waferholding unit 34 are adjusted so that the whole of the front side 11 a ofthe wafer 11 is covered with the liquid resin 27. Thereafter,ultraviolet light is applied from the ultraviolet light source 26 towardthe liquid resin 27 to thereby cure the liquid resin 27. Accordingly, asshown in FIG. 4C, the liquid resin 27 is formed into a protective member29 fully covering the protective film 21, and this protective member 29is fixed to the front side 11 a of the wafer 11. Thusly, the protectivefilm 21 on the front side 11 a of the wafer 11 is fully covered with theprotective member 29 formed from the liquid resin 27, thereby fixing theprotective member 29 through the protective film 21 to the front side 11a of the wafer 11. Further, the sheet 25 is fixed to the protectivemember 29.

After performing the protective member fixing step, the grinding step isperformed to grind the back side 11 b of the wafer 11. FIG. 5A is aschematic side view, partially in cross section, showing a manner ofgrinding the back side 11 b of the wafer 11, and FIG. 5B is a schematicsectional view of the wafer 11 processed by the grinding step.

The grinding step may be performed by using a grinding apparatus 42shown in FIG. 5A. The grinding apparatus 42 includes a holding table(chuck table) 44 for holding the wafer 11 under suction. The holdingtable 44 is connected to a rotational drive source (not shown) such as amotor. Accordingly, the holding table 44 is adapted to be rotated aboutits axis substantially parallel to a vertical direction, by operatingthis rotational drive source. A moving mechanism (not shown) is providedbelow the holding table 44, so as to move the holding table 44 in ahorizontal direction. The holding table 44 has an upper surface, a partof which is formed as a holding surface 44 a for holding under suctionthe sheet 25 fixed through the protective member 29 to the wafer 11. Theholding surface 44 a is connected through a suction passage (not shown)to a vacuum source (not shown), in which the suction passage is formedinside the holding table 44. Accordingly, by applying a vacuum generatedfrom the vacuum source through the suction passage to the holdingsurface 44 a in the condition where the sheet 25 is in contact with theholding surface 44 a, the wafer 11 can be held through the sheet 25 andthe protective member 29 on the holding table 44 under suction.

A grinding unit 46 is provided, above the holding table 44. The grindingunit 46 includes a spindle housing (not shown) supported to an elevatingmechanism (not shown). A spindle 48 is rotatably supported in thespindle housing. A disk-shaped mount 50 is fixed to the lower end of thespindle 48. A grinding wheel 52 is mounted on the lower surface of themount 50, in which the grinding wheel 52 has substantially the samediameter as that of the mount 50. The grinding wheel 52 includes awheel, base 54 formed of metal such as stainless steel and aluminum. Aplurality of abrasive members 56 are fixed to the lower surface of thewheel base 54 so as to be annularly arranged along the outercircumference of the wheel base 54. A rotational drive source (notshown) such as a motor is connected to the upper end (base end) of thespindle 48. Accordingly, the grinding wheel 52 fixed to the spindle 48is adapted to be rotated about its axis substantially parallel to avertical direction, by operating this rotational drive source to producea rotational force. A nozzle (not shown) for supplying a grinding fluidsuch as pure water to the wafer 11 is provided inside or in the vicinityof the grinding unit 46.

In the grinding step, the wafer 11 is first held on the holding table 44of the grinding apparatus 42 under suction. More specifically, the wafer11 is first placed on the holding table 44 a of the holding table 44 inthe condition where the sheet 25 fixed through the protective member 29to the wafer 11 is in contact with the holding surface 44 a. That is,the back side 11 b of the wafer 11 is exposed upward in this condition.Thereafter, the vacuum source is operated to apply a vacuum to theholding surface 44 a of the holding table 44. Accordingly, the wafer 11is held through the sheet 25 and the protective member 29 on the holdingtable 44 under suction in the condition where the back side 11 b of thewafer 11 is exposed upward. Thereafter, the holding table 44 is moved tothe position below the grinding unit 46. In this condition, both theholding table 44 and the grinding wheel 52 are rotated and the spindlehousing (the spindle 48 and the grinding wheel 52) is then lowered assupplying the grinding fluid to the back side 11 b of the wafer 11 asshown in FIG. 5A.

The lowering speed (feed speed) of the spindle housing is adjusted sothat the lower surface of each abrasive member 56 is pressed against theback side lib of the wafer 11 by a suitable force. Accordingly, the backside lib of the wafer 11 can be ground by the grinding wheel 52 tothereby reduce the thickness of the wafer 11. When the thickness of thewafer 11 is reduced to a predetermined thickness (finished thickness) asshown in FIG. 5B, this grinding step is finished. While one set ofgrinding unit 46 is used to grind the back side lib of the wafer 11 inthis preferred embodiment, two or more sets of grinding units may beused to grind the back side 11 b of the wafer 11. For example, a firstset of abrasive members each containing large-sized abrasive grains maybe first used to perform coarse grinding on the back side 11 b of thewafer 11, and a second set of abrasive members each containingsmall-sized abrasive grains may be next used to perform fine grinding onthe back side 11 b of the wafer 11. In this case, the flatness of theback side lib of the wafer 11 can be improved without greatly increasingthe time required for grinding.

After performing the grinding step, the peeling step is performed topeel the protective film 21 and the protective member 29 from the wafer11 thinned by the grinding step. FIG. 6 is a schematic sectional viewshowing a manner of peeling the protective film 21 and the protectivemember 29 from the wafer 11.

In the peeling step, a wafer holding unit 62 having a holding surface 62a is used to hold the wafer 11. That is, the back side 11 b of the wafer11 is held on the holding surface 62 a of the wafer holding unit 62. Thewafer holding unit 62 may be of a vacuum suction type such that a vacuumis used to hold the wafer 11 on the holding surface 62 a under suctionor may be of an electrostatic attraction type such that an electrostaticforce is used to hold the wafer 11 on the holding surface 62 a. Afterholding the wafer 11 on the holding surface 62 a of the wafer holdingunit 62, a peeling unit 64 is used to peel the protective member 29 andthe protective film 21. More specifically, a peripheral portion of thesheet 25 is gripped by the peeling unit 64. Thereafter, the waferholding unit 62 and the peeling unit 64 are relatively moved so that theperipheral portion of the sheet 25 is moved away from the wafer 11 asshown in FIG. 6. Accordingly, all of the protective film 21, theprotective member 29, and the sheet 25 can be peeled together from thewafer 11 as shown in FIG. 6.

In the wafer processing method according to the above preferredembodiment mentioned above, the protective film 21 is first brought intoclose contact with the front side 11 a of the wafer 11 on which thedevices 15 each having the bumps (asperities) 17 are formed in such amanner as to follow the shape of each bump 17. Thereafter, theprotective film 21 is covered with the protective member 29 formed fromthe liquid resin 27 curable by ultraviolet light (external stimulus),thereby fixing the protective member 29 through the protective film 21to the front side 11 a of the wafer 11. Accordingly, by forming theprotective member 29 having a suitable thickness, the asperities due tothe bumps 17 formed on the front side 11 a of the wafer 11 can besufficiently absorbed.

In the wafer processing method according to this preferred embodiment,the protective film 21 is not bonded to the device area lid of the wafer11, but is merely in close contact with the device area 11 d.Accordingly, the protective member 29 and the protective film 21 can besimply peeled from the wafer 11 without the need for any extensive workdedicated to peeling, such as immersion of the wafer 11 in a solution orheating of the wafer 11 at high temperatures. Thus, according to thispreferred embodiment, it is possible to provide a wafer processingmethod which can exhibit the effects that the influence of theasperities due to the bumps 17 present, on the front side 11 a of thewafer 11 can be sufficiently suppressed in grinding the back side lib ofthe wafer 11 and that the peeling operation after grinding can also besimply performed.

Further, in the wafer processing method according to this preferredembodiment, the protective film 21 is pressed against the front side 11a of the wafer 11 through the liquid 23 supplied, to the front side 11 aof the wafer 11. Accordingly, it is possible to prevent that air may beleft between the wafer 11 and the protective film 21, thereby reliablybringing the protective film 21 into close contact with the front side11 a of the wafer 11. As a result, although the protective film 21 doesnot have adhesion by an adhesive (paste), there is no possibility thatthe protective film 21, and the protective member 29 may be peeled fromthe wafer 11 in grinding the wafer 11.

The present invention is not limited to the above preferred embodiment,but various modifications may be made. For example, while the liquidresin 27 is a liquid resin curable by ultraviolet light as externalstimulus in this preferred embodiment, another type of liquid resincurable by any external stimulus (e.g., heat) other than ultravioletlight may be used as the liquid resin 27.

Further, while the circular protective film 21 having a diametersubstantially equal to that of the wafer 11 is used in this preferredembodiment, the diameter of the protective film 21 may be smaller thanthe diameter of the wafer 11. For example, the diameter of theprotective film 21 may correspond to the diameter of the device area lidof the wafer 11. In this case, the protective member 29 formed from theliquid resin 27 adheres directly to the peripheral marginal area lie ofthe wafer 11. Accordingly, although the protective film 21 does not haveadhesion by an adhesive (paste), the protective film 21 and theprotective member 29 can be firmly fixed to the wafer 11.

Further, in this preferred embodiment, the wafer 11 is pressed throughthe protective film 21 against the liquid resin 27 applied to the sheet25, thereby fixing the protective member 29 to the wafer 11. As amodification, the liquid resin 27 may be dropped onto the wafer 11 orthe protective film 21 without using the sheet 25, thereby fixing theprotective member 29 to the wafer 11. In this case, the exposed surfaceof the protective member 29 is preferably flattened by using a surfaceplaner or the like. By flattening the exposed surface of the protectivemember 29 to be held on the holding table 44 in grinding the wafer 11,the back side 11 b of the wafer 11 as a work surface can be ground flatin the grinding step.

Further, while the protective film 21 is softened by the heat, appliedfrom the heater 20 in the close contact making step in this preferredembodiment, softening of the protective film 21 is not essential in theclose contact making step. Further, the protective film 21 may besoftened by any methods other than heating by the heater 20.

Further, while all of the protective film 21, the protective member 29,and the sheet 25 are peeled together from the wafer 11 by simplygripping the peripheral portion of the sheet 25 and moving it away fromthe wafer 11 in the peeling step according to this preferred embodiment,another method may be used to peel the protective film 21, theprotective member 29, and the sheet 25 from the wafer 11. FIG. 7 is aschematic sectional view showing a manner of peeling the protective film21, the protective member 29, and the sheet 25 from the wafer 11 in apeeling step in a wafer processing method according to a firstmodification. The other steps in the wafer processing method accordingto the first modification may be the same as those in the waferprocessing method according to the above preferred embodiment.

In the peeling step according to the first modification, the back side11 b of the wafer 11 is held on the holding surface 62 a of the waferholding unit 62 as shown in FIG. 7. The wafer holding unit 62 may be ofa vacuum suction type such that a vacuum is used to hold the wafer 11 onthe holding surface 62 a under suction or may be of an electrostaticattraction type such that an electrostatic force is used to hold thewafer 11 on the holding surface 62 a. In the first modification, aheater 66 is provided inside the wafer holding unit 62 as shown in FIG.7.

After holding the wafer 11 on the holding surface 62 a of the waferholding unit 62, a peripheral portion of the sheet 25 is gripped by thepeeling unit 64. Thereafter, the wafer holding unit 62 and the peelingunit 64 are relatively moved so that the peripheral portion of the sheet25 is moved away from the wafer 11 as shown in FIG. 7. At this time, theheater 66 is operated to heat the liquid 23 left between the protectivefilm 21 and the wafer 11, thereby vaporizing the liquid 23. Thus, all ofthe protective film 21, the protective member 29, and the sheet 25 canbe peeled together from the wafer 11 as shown in FIG. 7.

In the wafer processing method according to the first modification, theliquid 23 left between the protective film 21 and the wafer 11 is heatedto be vaporized by operating the heater 66, so that the protective film21 can be easily peeled from the wafer 11.

FIG. 8 is a schematic sectional view showing a manner of peeling theprotective film 21, the protective member 29, and the sheet 25 from thewafer 11 in a peeling step in a wafer processing method according to asecond modification. The other steps in the wafer processing methodaccording to the second modification may be the same as those in thewafer processing method according to the above preferred embodiment.

The peeling step according to the second modification may be performedby using a vacuum chamber 72 shown in FIG. 8. The vacuum chamber 72includes a casing member 72 a having an upper opening having a sizeallowing the pass of the wafer 11 and a door member 72 b for closing theupper opening of the casing member 72 a. The casing member 72 a isconnected through an outlet pipe 74 and a valve 76 to a vacuum source(not shown). The casing member 72 a is also connected to an inlet pipe78 and a valve 80 for introducing the outside air (atmospheric air) intothe vacuum chamber 72.

The door member 72 b is formed with a vertically extending through hole72 c. A wafer holding unit 84 is inserted through the through hole 72 cwith a hermetic bearing 82 interposed therebetween, so that the waferholding unit 84 is vertically movably supported to the door member 72 bby the hermetic bearing 82. The wafer holding unit 84 has asubstantially flat lower surface 84 a as a holding surface larger indiameter than the wafer 11. The wafer holding unit 84 may be of anelectrostatic attraction, type such that an electrostatic force is usedto hold the wafer 11 on the lower surface 84 a. Further, a heater 86 isprovided inside the wafer holding unit 84. A peeling unit 88 is providedin the vicinity of the wafer holding unit 84.

In the peeling step according to the second modification, the back side11 b of the wafer 11 is held on the lower surface 84 a of the waferholding unit 84. Thereafter, the door member 72 b is closed to cover theupper opening of the casing member 72 a, and the valve 80 is closed.Thereafter, the valve 76 is opened to thereby evacuate the inside spaceof the vacuum chamber 72. Thereafter, a peripheral portion of the sheet25 is gripped by the peeling unit 88, and the wafer holding unit 84 andthe peeling unit 88 are relatively moved so that the peripheral portionof the sheet 25 is moved away from the wafer 11. At this time, theheater 86 may be operated to heat the liquid 23 left between theprotective film 21 and the wafer 11, thereby vaporizing the liquid 23.Thus, all of the protective film 21, the protective member 29, and thesheet 25 can be peeled together from the wafer 11 as shown in FIG. 8.

In the wafer processing method according to the second modification, theprotective film 21 is peeled from the wafer 11 under vacuum.Accordingly, the liquid 23 left between the protective film 21 and thewafer 11 is vaporized in the peeling step, so that the protective film21 can be easily peeled.

Further, while the compressed, air is discharged toward the uppersurface of the protective film 21 to thereby press the protective film21 against the front side 11 a of the wafer 11 in the above preferredembodiment, another method may be used to press the protective film 21against the wafer 11. FIGS. 9A and 9B are schematic sectional views forillustrating a close contact making step in a wafer processing methodaccording to a third modification.

The wafer processing method according to the third modification includesa liquid supplying step, in which the liquid 23 is preferably suppliedto at least an area where the close contact between the protective film21 arid the wafer 11 is started. Accordingly, in the next close contactmaking step, the protective film 21 can be reliably brought into closecontact with the front side 11 a of the wafer 11 so as to prevent thepossibility that air may be left between the wafer 11 and the protectivefilm 21. The other steps in the wafer processing method according to thethird modification may be the same as those in the wafer processingmethod according to the above preferred embodiment or the abovemodifications.

In the close contact making step according to the third modification,the back side 11 b of the wafer 11 is held on a holding surface 92 a ofa holding table 92. The basic configuration of the holding table 92 maybe the same as that of the holding table 44 except that a heater 94 isprovided inside the holding table 92 in the third modification. Afterholding the wafer 11 on the holding table 92, the protective film 21previously held on the lower surface of a release sheet 31 is opposed tothe front side 11 a of the wafer 11. Thereafter, a pressure roller 96 isused to apply a downward pressure to the upper surface of the releasesheet 31, thereby pressing the protective film 21 against the front side11 a of the wafer 11 as shown in FIG. 9A. At this time, the heater 94 ispreferably operated to heat the protective film 21, thereby softeningthe protective film 21. Accordingly, the protective film 21 can bebrought into close contact with the front side 11 a of the wafer 11 withthe liquid 23 interposed therebetween. Finally, the release sheet 31 isreleased from the protective film 21 as shown in FIG. 9B. As amodification, this close contact making step using the pressure roller96 may be performed in a vacuum chamber.

The present invention is not limited to the details of the abovedescribed preferred embodiment. The scope of the invention is defined bythe appended claims and all changes and modifications as fall within theequivalence of the scope of the claims are therefore to be embraced bythe invention.

What is claimed is:
 1. A wafer processing method comprising: a liquidsupplying step of supplying a liquid to the front side of a wafer onwhich a central device area and a peripheral marginal area surroundingsaid device area are formed, a plurality of devices each havingasperities being formed in said device area; a close contact making stepof pressing a protective film against the front side of said wafer withsaid liquid interposed therebetween after performing said liquidsupplying step, thereby bringing said protective film into close contactwith the front side of said wafer so as to follow said asperities ofeach device formed on the front side of said wafer; a protective memberfixing step of covering said protective film with a protective memberformed from a liquid resin curable by external stimulus after performingsaid close contact making step, thereby fixing said protective memberthrough said protective film to the front side of said wafer; a grindingstep of holding said protective member fixed to said wafer on a holdingsurface of a chuck table in the condition where the back side of saidwafer is exposed after performing said protective member fixing step,and next grinding the back side of said wafer to thereby reduce thethickness of said wafer; and a peeling step of peeling said protectivefilm and said protective member from said wafer after performing saidgrinding step.
 2. The wafer processing method according to claim 1,wherein said peeling step includes the step of heating said liquid leftbetween said protective film and the front side of said wafer to therebyvaporize said liquid.
 3. The wafer processing method according to claim1, wherein said peeling step includes the steps of loading said waferwith said protective member into a vacuum chamber and next evacuatingsaid vacuum chamber to thereby vaporize said liquid left between saidprotective film and the front side of said wafer.
 4. The waferprocessing method according to claim 1, wherein said liquid supplyingstep includes the step of supplying said liquid to a central portion ofthe front side of said wafer.
 5. The wafer processing method accordingto claim 1, wherein said protective film has a first surface and asecond surface opposite to said first surface, said first surface beingopposed to said wafer; said close contact making step including the stepof discharging a gas toward said second surface of said protective filmto thereby press said protective film against the front side of saidwafer.
 6. The wafer processing method according to claim 1, wherein saidclose contact making step includes the step of using a pressure rollerto thereby press said protective film against the front side of saidwafer.
 7. The wafer processing method according to claim 1, wherein saidprotective member fixing step includes the steps of applying said liquidresin to a flat sheet, next pressing said wafer against said liquidresin through said protective film to thereby fully cover saidprotective film with said liquid resin, and next applying said externalstimulus to said liquid resin to thereby cure said liquid resin, therebyforming said protective member from said liquid resin and fixing saidprotective member to said wafer.